Improved image quality? Absolutely. However, the D800 causes you to potentially adjust your shooting style and make sure you're using proper technique - there are so many pixels that slight camera shake can show up in the form of slight blurring on edges of image area. I love the increase in range and quality.
With my step up to D800 I also decided to get away from zoom lenses and concentrate on prime lenses due to inherent quality differential between prime and zooms. I have purchased the Nikon 85mm f/1.8G and the Nikon 28mm f/1.8G to complement the Nikon 50mm and 35mm lenses that I already owned. Now I'm looking for a 20mm and 105mm - all it takes is money and when you're retired - oh well, you know the story.
If I can supply more info or answer any questions send me a note at firstname.lastname@example.org and I'll be happy to help however I can.